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Swagelok Northwest (US)

Your Authorized Swagelok Sales and Service Center

O-ring Selection

Getting the right O-ring means getting the right hardness.

Proper O-rings selection is one of the most commonly overlooked decisions for sealing a fluid system because of their size, cost and visually unseen material difference. However, just like your tubing, fittings, and valves, material selection makes a difference in how your system performs.

O-rings are manufactured using pliable material such as Silicone, Buna-N and Ethylene-Propylene and are expressed in hardness on the Shore A scale, which is measured with a durometer. The number may be specified as "60 Shore A", or commonly as "60 durometer", which signifies the relative hardness on a scale from 10A to 100A.

Because of the many different materials O-rings are produced from, system performance can yield different results under various conditions. For example, our SK series ball valve comes standard with a low-temperature fluorocarbon FKM O-ring that provides long-term service where corrosive additives can cause other elastomers to swell or degrade. However, in many applications, replacing the O-ring in the SK series with a 90 durometer Buna or Ethylene Propylene can improve vacuum sealing performance.

The following sections includes the most commonly materials used for the O-rings, their working temperature, the hardness scores, as well as the limitations of those materials.

Silicone

Hardness (Shore A): 20-80

Working temperature: -65° to 450°F

Offers good resistance to extreme high and low temperatures. It has excellent resistance to oxygen, ozone, UV and many chemicals. Low tensile strength, poor wear resistance and tear strength. Typically limited to static applications.


Aflas

Hardness (Shore A): 40-90
Working temperature: -10° to 400°F

Aflas® is a trade name for tetrafluoroethylene propylene copolymer (TFE/P). Offers excellent chemical resistance to automotive lubricants, battery acids, jet fuels and oil field applications. The most common use is in plastic valves in ozone water treatment systems, where it is excellent.  

Buna-N

Hardness (Shore A): 40-90
Working temperature: -40° to 250°F 

Recommended for general purpose sealing of water, petroleum oils, solvents and some alkalis. It is superior to most other elastomers with regard to compression set, abrasion and tear resistance.

  

 


Butyl

Hardness (Shore A): 30-90
Working temperature: 50° to 250°F 

Offers very low permeability and chemical resistance to hot water and steam up to 250°F, brake fluids, some acids, alcohols, and many other chemicals. It is not compatible with mineral oil, fuels, or chlorinated hydrocarbons.   

 
 

Ethylene-Propylene Rubber (EPR)

Hardness (Shore A): 30-95 
Working temperature: -50° to 250°F 

Excellent resistance to atmospheric ageing and ozone, phosphate ester hydraulic fluids, brake fluids, weak acids and bases. Has good wear resistance. Attacked by oils and petroleum lubricants. 


Fluorocarbon (VDF/HFP)

Hardness (Shore A): 55-90 
Working temperature: -20° to 400°F 

Provides chemical resistance to a wide range of chemicals including mineral acids, salt solutions, chlorinated hydrocarbons and petroleum oils. Not recommended for use with steam or ammonia.

 


Fluorosilicone


Hardness (Shore A): 40-80 
Working temperature: -100° to 350°F 

This elastomer is known for its retention of flexibility, resilience and tensile strength over a wide temperature range. However, it is not known for its chemical resistance. Typically limited to static applications.


Perfluoroelastomer


Hardness (Shore A): 65-90 
Working temperature: -15° to 428°-600°F 

Offers chemical resistance that is far superior to most other elastomers. It can have limited low temperature use and high compression set.  
 
 
  
 
 

Polychloroprene (Neoprene)

Hardness (Shore A): 45-65 
Working temperature: -65° to 212°F 

First introduced by DuPont as Neoprene. It resists degradation from sun, ozone and weather and performs well in contact with hydrocarbon oils and many chemicals. It has excellent physical toughness.
 
 

Silicone


Hardness (Shore A): 20-80 
Working temperature: -65° to 450°F 

Offers good resistance to extreme high and low temperatures. It has excellent resistance to oxygen, ozone, UV and many chemicals. Low tensile strength, poor wear resistance and tear strength. Typically limited to static applications.